True 3D video displays target physical duplication of volume filling light of a scene. If a perfect duplication can be achieved, any observer, human or not, interacting with the duplicate light will see an exact ghost-like duplicate of the original scene. Most of the techniques commonly used today for 3D video are based on stereoscopic technique, as in commercial 3D movies. Even though multi-view video techniques are better than stereoscopy, these techniques are still far from ideal true 3D. The only true 3D technique is the holography. An overview of different 3D display techniques can be found in P. Benzie, J. Watson, P. Surman, I. Rakkolainen, K. Hopf, H. Urey, V. Sainov and C. von Kopylow, “A Survey of 3DTV Displays: Techniques and Technologies”, IEEE Tran. on Circuits and Systems for Video Technology, vol 17, no 11, pp 1647-1658, November 2007. A survey on existing holographic displays can be found in F. Yara, H. Kang and L. Onural, “State of the Art in Holographic Displays: A Survey”, J. of Display Technology, vol 6, no 10, pp 443-454, October 2010. One of the major problems of the state-of-the art electro-holographic video cameras or displays is the required high spatial bandwidth (resolution) of the underlying electro-optical device. Holographic patterns are typically complicated fringe patterns where the fringes have very fine details; the detail is in the order of the wavelength and therefore, is in the micrometer range for optical holography. In addition to the high spatial bandwidth, a rather large size, ranging from a few square centimeters to many square decimeters, is needed for a satisfactory viewing experience. Such a fine resolution over a rather large area means a very large space-bandwidth product. Therefore, for a digital display, the device on which the holograms are electronically written must have very small pixel sizes (in the order of micrometers) that in turn, brings the number of such pixels to the order millions per square millimeter of the device. The same is also true for the camera: the electro-optical capturing device that captures the holographic fringe pattern must have a high spatial bandwidth (resolution) and a very large space-bandwidth product. The difficulty in the design and manufacturing of such high-resolution display or capture devices is one of the main obstacles that prevent consumer quality holographic video displays. The effect of the resolution on the display is one of the important issues to consider and it can be analyzed as given in L. Onural, F. Yara and H. Kang, “Digital Holographic Three-Dimensional Video Displays”, Proc. of the IEEE, vol 99, no 4, pp 576-589, April 2011. Simply, each small patch on the display device is a local diffractor that distributes the incident light to different directions as it passes (transmissive case) or reflects (reflective case) from that patch. The resolution is directly related to the diffraction angle: larger resolutions result in finer patterns which in turn result in larger diffraction angles; therefore, a large resolution is needed to distribute outgoing light within a larger angle. The size of this angle also determines the viewing angle of the observer. The same is also true for capture devices: larger angles of incidence results in high resolution fringes to capture. Therefore, the resolution, both at the display or the capture, is directly related to viewing and capturing angles.
A curved mirror based holographic display device which overcomes the abovementioned difficulties associated with high resolution (wide viewing angle) requirement problem is disclosed in a prior patent application by L. Onural which has been filed on Dec. 8, 2014 and has the application number “PCT/TR2014/000492” and the title of “A System and Method for Displaying and Capturing Holographic True 3D Images”.
The invention disclosed here in this document, is another solution to the same problem. Now a phase plate which has a specified pattern of groves on it is used instead of the curved mirror. As a consequence, the size and the geometry is significantly simplified.
An example of a holographic 3D image display, which utilizes a diffraction grating sandwiched between lens arrays to effectively yield a complex valued spatial light modulation, is disclosed in worldwide patent WO2013/187704. Accordingly, the phase and the amplitude of light may be modulated simultaneously. The modulator may further comprise a phase plate and a polarizing plate which are disposed between the spatial light modulator and the first lens array.